The need to convert a digital signal to a radio frequency (RF) signal arises in a wide variety of military and commercial applications. In these applications, a digital-to-RF converter is employed to convert a digital signal representative of digital data to a radio frequency signal. The radio frequency signal provides a radio frequency representation of the digital data which can be transmitted in order to communicate the digital data.
FIG. 1 is a block diagram of a conventional vector digital-to-RF modulator 10. The digital-to-RF modulator 10 receives a baseband signal in the form of an inphase signal S.sub.I (t) representative of an inphase component of the baseband signal and a quadrature signal S.sub.Q (t) representative of a quadrature component of the baseband signal. The inphase signal S.sub.I (t) and the quadrature signal S.sub.Q (t) are applied to baseband processors 12 and 14, respectively. The baseband processors 12 and 14 perform steps such as bit mapping, symbol translation, and digital-to-analog conversion.
FIG. 2 is a block diagram illustrating the steps which may be performed by a baseband processor. The baseband processor receives a signal, such as the inphase signal or the quadrature signal, and applies the received signal to a shift register 16. The shift register 16 forms a multi-bit data word based upon the received signal. The data word is applied to a processor/translator 18 which performs steps of baseband processing and/or symbol translation. The output of the processor/translator 18 is applied to a digital-to-analog converter 20 which forms an analog signal representative of the data word.
Turning back to FIG. 1, the analog signal produced by the baseband processor 12 is modulated by a cosine wave signal, indicated by cos(.omega.t), using a mixer 22. Similarly, the analog signal produced by the baseband processor 14 is modulated by a sine wave signal, indicated by sin(.omega.t), using a mixer 24. The two modulated signals produced by the mixers 22 and 24 are combined by a summing block 26 to form the modulated radio frequency signal.
A disadvantage of the above-described methods and systems for digital-to-RF conversion is the limited rate of conversion which results from performing steps of baseband processing and digital-to-analog conversion. The rate limitation constrains the flexibility and versatility of present digital-to-RF converters.